Quarterly Financial Data - Unaudited (Tables)

12 Months Ended

Dec. 31, 2017

Dec. 31, 2016

Quaterly Financial Data Unaudited [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

2017	Fourth		Third		Second		First
Revenues	$	5,638	$	5,314	$	5,250	$	5,185
Operating income	$	2,013	$	1,953	$	1,787	$	1,594
Net income	$	8,462	$	1,042	$	958	$	838

2016	Fourth		Third		Second		First
Revenues	$	5,310	$	5,167	$	4,585	$	4,767
Operating income	$	1,813	$	1,880	$	1,487	$	1,505
Net income	$	993	$	1,020	$	772	$	784